Free flowing powder

ABSTRACT

The present invention relates to a free flowing powder composition with a particle size at most 800 μm comprising: (a) 100 parts by weight of one or more styrenic block copolymers, at least one of which being a block copolymer (a1) comprising at least one block S having a glass transition temperature Tg above 25° C., which contains polymerized units of a vinylaromatic monomer and at least one elastomeric block B/S having a Tg below 25° C., which contains polymerized units of both a vinylaromatic monomer and a conjugated diene in random sequence, wherein the phase volume ratio of block S to block B/S is chosen so that the amount of the rigid phase in the total block copolymer is from 1 to 40% by volume and wherein the amount of the conjugated diene is less than 50% by weight on the whole of the copolymer; optionally (b) 0 to 200 parts by weight of plasticizing oil; optionally (c) 0 to 200 parts by weight of a compatibilizing resin; and optionally (d) a dusting agent in an amount of from 0 to 10% by weight based on total weight of composition. It also relates to a process for the preparation thereof and to homogeneous layers derived therefrom.

FIELD OF THE INVENTION

The present invention relates to a free flowing powder composition, to aprocess for the preparation thereof and to homogeneous layers derivedtherefrom.

BACKGROUND OF THE INVENTION

Dashboard skins of instrument panels, console boxes, door trims, andother interior trims in automobiles have been made by slush moldingprocesses. In these processes free flowing powder composition of athermoplastic elastomer are fused together. The free flowing powdertypically has a maximum particle size of 800 μm. These skins are soft tothe touch, allow for leather graining and stitching, and permit greatdesign freedom.

Unlike injection or compression molding, no pressure is applied forshaping in powder molding processes. Therefore, the powdery material forpowder slush molding ideally has a high degree of fluidity in thepowdery state so as to attain the uniform adhesion of the material to amold having a complicated shape. It should also exhibit a low meltviscosity so that it can be molten and fluidized without pressing toform a film. Furthermore, it is desirable that the skin layer formed ona mold release easily from the mold after cooling.

Besides, in case of slush molding of dashboard skins, fusion of freeflowing powder is typically done at about 190° C. The fusion temperatureshould hence not be higher than about 190° C. On the other hand,dashboard skins and other automobile parts have to withstand 500 hoursaging at 130° C. and have a hardness of about 85 Shore A. Ideal freeflowing powders should hence have a fusion temperature in the range of130 to 190° C. Finally, according to present industrial standards,products made by slush molding should have tear strength higher than 50N/mm, tensile strength higher than 12 MPa, and elongation at breakhigher than 300%.

Up to now PVC powders are widely used in slush molding processes.Unfortunately, plasticizers used in PVC migrate from the end-product andlead to window fogging when used in interior parts in automobiles.Hence, there is a need for suitable alternatives for PVC powders.

Free flowing powder compositions have been described in European patentapplication No. 659,831 and International application No. 97/00294. Thepowder compositions described in these applications are very useful forobtaining homogeneous layers having a smooth surface. These layers canbe applied successfully for carpet backing, conveyor belts, bottle capsealants, etc. In practice, however, these powder compositions requirethe presence of a plasticizing agent to be fusible at ordinary fusiontemperatures (e.g. 120 to 190° C.). Accordingly, like PVC powder, thesepowder compositions may lead to fogging and are hence less suitable forslush molding of dashboard skins and similar products.

Powder material compositions designed for slush molding processes havealso been proposed in Japanese patent application No. Hei 7-82433 and inEuropean patent application No. 811,657. However, the former compositionis said (by the inventors of the latter composition) to suffer from oilbleed out. The latter composition, on the other hand, employs aplasticizer (process oil, trademark DIANA). This may again lead towindow fogging.

It would therefore still be desirable to find a thermoplastic elastomercomposition, for use in powder slush molding, but also in otherapplications such as carpet backing and paper and board coating, thatmay be free of said oil component. It would also be desirable to havesuch compositions, free of oil or low in oil content, that meet theother industrial standards for slush molded products.

SUMMARY OF THE INVENTION

Surprisingly, thermoplastic elastomer compositions, based on styrenicblock copolymers have been found that meet the above requirements.

Accordingly, the present invention provides a free flowing powdercomposition with a particle size of at most 800 μm comprising:

-   (a) 100 parts by weight of one or more styrenic block copolymers, at    least one of which being a block copolymer (a1) comprising at least    one block S having a glass transition temperature Tg above 25° C.,    preferably above 50° C., which contains polymerized units of a    vinylaromatic monomer and form the rigid phase and at least one    elastomeric block B/S having a Tg below 25° C., preferably below 5°    C., which contains polymerized units of both a vinylaromatic monomer    and a conjugated diene in random sequence and forms the soft phase,    wherein the phase volume ratio of block S to block B/S is chosen so    that the amount of the rigid phase in the total block copolymer is    from 1 to 40% by volume and wherein the amount of the conjugated    diene is less than 50% by weight on the whole of the copolymer;    optionally-   (b) 0 to 200, preferably 0 to 70, parts by weight of plasticizing    oil; optionally-   (c) 0 to 200, preferably 0 to 70, parts by weight of a resin that is    compatible with either the rigid phase (c1) or the soft phase (c2);    and optionally-   (d) a dusting agent in an amount of from 0 to 10% by weight,    preferably 1 to 5% by weight, based on total weight of composition.

DETAILED DESCRIPTION OF THE INVENTION

With the expression “free flowing powder composition” used throughoutthis specification is meant a powder (made by milling, micropelletizing,or similar technique) of which the particles consist of a composition asdefined above and of which the particles do not adhere to one another.

The size of the powder particles is expressed in terms of the particles'diameter. In general, this size is determined by sieving and isindependent of the shape of the particle.

The particle size should always be 800 μm or less, and preferablysmaller than 600 μm. In slush molding, the particle size is preferablysmaller still, say smaller than 300 μm with an average particle size of100 μm. In other applications, such as for instance a carpet backing,the powder particles do not need to be very small. For such applicationsparticle size preferably lies between 100 and 700 μm, and even morepreferably between 150 and 600 μm.

The styrenic block copolymer (a1) found to be extremely suitable inthermoplastic elastomer compositions for powder slush molding is apolymer that has a ‘soft’ mid-block that resembles a ‘statistical’copolymer of the vinylaromatic monomer and the conjugated diene (molarratio of vinylaromatic monomer to conjugated diene of about 1). Thispolymer preferably has a glass transition temperature (Tg) in the rangeof −40° C.A5° C. (soft phase) and a Tg in excess of about 60° C. (rigidphase). The block copolymer suitably has a melt flow rating (MFR) at200° C./5 kg in the range of 5 to 20 dg/min, preferably 10 to 15 dg/min.Suitable block copolymers have an order-disorder transition temperature(ODT, the temperature at which the blocks are sufficiently compatible toform a single phase) in the range of 100 to 200° C., preferably in therange of 120 to 190° C., preferably about 145° C. This component may beprepared according to anyone of the references U.S. Pat. No. 3,700,633;EP-A-0,398.758; or U.S. Pat. No. 6,031,053. The contents of theseapplications are enclosed by reference.

Component (a) may, and preferably does comprise one or more furtherstyrenic block copolymers (a2). In the event one or more blockcopolymers (a2) are present, then they are comprised in a weight/weightratio (on all styrenic block copolymers (a)) of (a1) to (a2) of 5:95 to95:5, preferably 10:90 to 90:10, more preferably of 20:80 to 80:20.

The further block copolymer (a2) may in principle be any block copolymercomprising at least one poly(vinylaromatic monomer) block and at leastone hydrogenated or unhydrogenated poly(conjugated diene) block. If goodheat-aging resistance, weatherability and resistance to oxidation isdesired, then selectively hydrogenated block copolymers are preferred.This may for instance be desired when recycling of the final product bymeans of heating is foreseen. On the other hand, unhydrogenated blockcopolymers may be preferred for less demanding applications.

The or each further block copolymer may have a linear, radial orstar-shaped structure. One preferred type of block copolymer however, isa linear block copolymer comprising two poly(vinylaromatic monomer)endblocks and one hydrogenated or unhydrogenated poly(conjugated diene)midblock (S-B-S, and S-B*-S respectively, wherein B* represents a[partially] hydrogenated B block). Apart from the main monomer, polymerblocks S and B may contain small amounts, i.e. up to 20% by weight butpreferably less than 10% by weight, of one or more other monomers whichare copolymerizable with the said main monomer. Component (a) may alsocomprise mixtures of different block copolymers, for instance anS-B/S-B-S block copolymer mixture with S and B as defined above inaddition to the styrenic block copolymer (a1) defined in the claim.

For all types of styrenic block copolymers (a) it is preferred that thevinylaromatic monomer is styrene and the conjugated diene is eitherbutadiene or isoprene. Alternatives, however, includealpha-methylstyrene, para- meta- or ortho-R—(O)-styrene (wherein ‘R’represents an alkyl group containing 1 to 8 carbon atoms),vinylnaphthalene and the like. Suitable conjugated dienes furtherinclude piperylene. The styrenic block copolymers (a) may also bearfunctional groups.

The apparent molecular weight of the block copolymer (a), i.e. themolecular weight as determined by gel permeation chromatography usingpolystyrene calibration standards, may vary over a broad range andsuitably lies within the range of from 25,000 to 1,000,000, preferably50,000 to 500,000. In the event of branched or star-shaped blockcopolymers the apparent molecular weight may even exceed 1,000,000.

The further block copolymers (a2) may be produced by any well knownpolymerization process, such as e.g. disclosed in U.S. Pat. Nos.3,322,856; 3,231,635; 4,077,893; 4,219,627 and 4,391,949.

Examples of commercially available block copolymers, which may be usedin the powder composition according to the present invention, includethe various STYROFLEX BX grades as component (a1), e.g., STYROFLEX BX6105, and the various KRATON D, G or FG grades as component (a2).

Examples of a suitable linear SBS copolymers are KRATON D-1101, KRATOND-1102, KRATON D-4271. KRATON D-1107 is an example of a linear SIS blockcopolymer. An example of a suitable styrene-isoprene multi-armed blockcopolymer is KRATON D-1320X. Examples of commercially availableselectively hydrogenated S-B*-S block copolymers are KRATON G 1650,1651, 1652 and 1654. (STYROFLEX and KRATON are trademarks).

The composition of the present invention may, but need not comprise aplasticizer oil. Mineral oils, both naphthenic and paraffinic oils, orlow molecular weight polybutylene polymers may be used as theplasticizing oil. Examples of suitable plasticizers are SHELLFLEX 371and 451, CATENEX 956 and TUFFLO 6204 (naphthenic oils), TUFFLO 6056(paraffinic oil) and the polybutylenes HYVIS 200, NAPVIS 30, NAPVIS D-10and EZL 675. (SHELLFLEX, CATENEX, TUFFLO, HYVIS and NAPVIS are trademarks.) Also very useful are poly-alpha-olefin based products, such ase.g. ETHYLFLO (ETHYLFLO is a trade mark), as well as other commerciallyavailable plasticizers, such as REGALREZ 1018 (REGALREZ is a trademark),ONDINA 68 (ONDINA is a trade mark) and V-OIL 7047 (V-OIL is a trademark). The plasticizer may be used in amounts of from 0 to 200 phr, forinstance from 0 to 70 phr. The abbreviation “phr” stands for parts byweight per 100 parts by weight of component (a).

As rigid phase compatible resin (cl) any resin known to be applicablefor this purpose may be used. Particularly suitable rigid phasecompatible resins include low molecular weight resins, largely derivedfrom alpha-methylstyrene. An example of such resin, which iscommercially available, is ENDEX 155 (ENDEX is a trade mark). Otherexamples include coumarone-indene resins, phenol-aldehyde resins andaromatic resins in general or clear or toughened PS (TPS 476 ex BASF).The rigid phase compatible resin may be used in an amount of from 0 to200 phr and preferably in an amount of from 0 to 70 phr, say about 50phr.

Alternatively, a soft phase (and/or midblock) compatible resin (c2) maybe used. As soft phase compatible resin (c2) any resin known to beapplicable for this purpose may be used. Particularly suitable softphase compatible resins include poly(α-olefins) such as poly(ethylene),poly(propylene) and copolymers of propylene and/or ethylene with otherolefins. Of these poly(α-olefins) those having a Melt Flow Rate (ASTM D1238)≧40 g/10 min (at 230° C. and a load of 2.16 kg) are particularlypreferred. A very suitable soft phase compatible resin (c2) is NOVOLENE1000 UC (polypropylene, NOVOLENE is a trademark). The soft phasecompatible resin may be used in an amount of from 0 to 200 phr andpreferably in an amount of from 0 to 70 phr.

The dusting agent (d) is very fine powder, i.e. a powder of which theaverage particle size lies between 1 nm and 100 μm, preferably between 5nm and 10 μm. In principle any such fine powder may be employed, but itis preferred that silica or calcium carbonate powder is used. Examplesof commercially available silica powders are AEROSIL R972 (averageparticle size about 16 nm), AEROSIL 200 (average particle size about 12nm), SIPERNAT, DUROSIL, DUREX and ULTRASIL. DURCAL 5 (average particlesize 6 μm) and MILLICARB (average particle size 3 μm) are examples ofcommercially available calcium carbonate powders. (AEROSIL, SIPERNAT,DUROSIL, DUREX, ULTRASIL, DURCAL and MILLICARB are trade marks.)

The dusting agent may be used when the free flowing powder compositionis made by milling. For instance, it may be made in an amount of from0.1 to 10% by weight, preferably from 1 to 5% by weight, based on totalweight of composition.

In addition to the components described above, the free flowing powdercomposition of the present invention may further comprise from 0 to 500phr, preferably from 0 to 300 phr and more preferably from 0 to 250 phr,of a filler. As the filler any filler material known in the art may beused. Hence, suitable fillers include calcium carbonate, aluminumsilicate, clays, talcs, silica and the like. Also very useful arereground polymeric waste, such as e.g. vulcanized rubber powder,recycled polyurethane or recycled carpets. Calcium carbonate, aluminumoxide (alumina), magnesium hydroxide, barium sulfate and silica areparticularly useful as the filler material. Of these, calcium carbonateand silica are most preferred.

The free flowing powder composition of the present invention may alsocontain a blowing agent. The presence of a blowing agent in the finalfree flowing powder composition may be desired if the powder compositionis to be applied in end-products having a particularly soft touch. Forinstance, blowing agent may be added in powder form by dry-blending withthe free flowing powder composition according to the present invention.Generally known blowing agents are for instance azodicarbonamide-basedcompounds and diphenyloxide-4,4′-disulphohydrazide. The latter iscommercially available under the trade name GENITRON OB (GENITRON is atrade mark), while the azodicarbonamide-based compounds are commerciallyavailable as GENITRON EPE, EPA and EPB. If present at all, the blowingagent may be present in the free flowing powder composition in amountsup to 3% by weight, preferably from 0.2 to 3% by weight, more preferablyfrom 0.5 to 2.5% by weight based on the total weight of composition.

In addition to the components described above, other conventionalingredients such as antioxidants, UV stabilizers, slipping agents, flameretarders and the like may be present. Generally, such ingredients arepresent in small quantities, i.e. up to 2% by weight based on the totalweight of composition. In this respect it is noted that severalinorganic filler materials listed above also may have flame retardingproperties and hence may be present in larger quantities than 2% byweight.

The present invention further relates to a process for the preparationof the free flowing powder composition as herein before described, saidprocess comprising the steps of:

-   (a) melt blending all components present in the free flowing powder    composition except the dusting agent and the blowing agent, if    present, followed by cooling;-   (b) granulating or pelletizing the composition resulting from step    (a);-   (c) cryogenically milling the granules or pellets resulting from    step (b); and optionally-   (d) dry-blending the dusting agent and/or the blowing agent with the    powder resulting from step (c).

Alternatively, a free flowing composition as herein before described maybe made by (a) melt blending all components present in the free flowingpowder composition except the dusting agent and the blowing agent, ifpresent; and (e) micropelletizing the composition resulting from step(a) using a die plate with a diameter ≦0.5 mm; followed by cooling, andoptionally (d) dry-blending the dusting agent and/or the blowing agentwith the micropellets resulting from step (e).

Cryogenic milling of the granules or pellets resulting from step (b) maybe performed through the conventional cryogenic milling techniques,wherein for instance liquid nitrogen often is used as the chillingmedium. For slightly larger particles, the said granules or pellets mayalso be milled using liquid carbon dioxide or freon as the chillingmedium.

The free flowing powder of the present invention can be used to form ahomogeneous layer having a smooth surface. In order to obtain suchlayer, the dry free flowing powder may first be brought onto a suitableunderground as a layer. Upon exposure to heat, the powder particles thenfuse and a homogeneous layer is formed. Accordingly, the presentinvention also embraces homogeneous layers obtainable by fusing the freeflowing powder composition described above.

Preferably, the fusing of the free flowing powder composition isrealized by heating a layer of the composition. A preferred method ofheating is subjecting the unfused powder composition to infraredradiation. However, other heating methods, such as flame-spraying orcontacting hot objects with the powder thus establishing fusion of thepowder particles at the surface of the said object, may be applied aswell. Fluidised bed and slush molding techniques are very useful in thelatter heating method.

It will be understood that instruments panels, console boxes, door trimsand other interior trims in automobiles prepared by slush molding of thepresent free flowing powder composition, as well as other shapedarticles containing a layer of the fused free flowing powdercomposition, such as carpets, conveyor belts or bottle cap sealants,also form part of the present invention.

The invention is further illustrated by the following examples.

Materials and Formulations

The materials used in this study are listed in the Table below.

Trade name Function Description and supplier KRATON G-1652 a2 S-E/B-Sblock copolymer, 30% w polystyrene content (PSC), low MW, SHELL KRATONG-1654 a2 S-E/B-S block copolymer, 31% w PSC, high MW, SHELL STYROFLEXa1 S-B/S-S block copolymer, 65% w BX 6105 PSC, high MW, BASF NOVOLEN1100UC c2 polypropylene, MFR (E) = 75 g/10 min, BASF ENDEX 155 c1Styrenic resin, ring and ball softening point = 153° C., HERCULESTINUVIN 327 UV stabilizer, CIBA-GEIGY IRGANOX 1010 anti-oxidant,CIBA-GEIGY high MW means Mn > 130.000; low MW means Mn < 80.000. MFR(E)means Melt flow rate at 190° C. with a 2.16 kg load.Pre-preparation

Compositions of various formulations were prepared on a WERNER andPFLEIDERER ZSK 25 co-rotating compounding twin screw extruder, operatingat temperature, settings between 145 and 245° C., after pre-blending ina PAPENMEIER dry-blender. The formulations of these compositions can befound in Table 1.

In typical free flowing powder applications, these compositions would beallowed to cool and subsequently be granulated. The granules would thenbe embrittled by putting them into a bath of liquid nitrogen and bepassed through a mill cooled to −95° C. For instance, the granulatedcompositions may be cryogenically milled in an ALPINE 160 UPZ FineImpact Mill.

However, for the assessment of the properties and the suitability of theformulations as free flowing powder, the actual preparation of freeflowing powder is not required. Rather, such properties have beenextrapolated from the results of the following modeling experiments.

MODELING EXPERIMENTS 1 TO 8

2 mm thick injection molded plates were made on a BATTENFELD BA 200injection molding machine and used to test the physical properties ofthese compositions.

The hardness was measured after 30 seconds indentation on a stack ofthree 2 mm thick injection molded test plates using the Shore A andShore D hardness durometers, following the ASTM D 2240-86 method.

Dumbbells, according to ISO-37, were cut from the conditioned injectionmolded test plates. Crosshead speed of the ZWICK Mechanical Tester was500 mm/min and the distance between the bench marks 20 mm. The tensileproperties were measured in the mold direction (MD) and perpendicular tothe mold direction (PMD).

ASTM D 624 was followed to determine tear strength on injection moldedsamples, in the MD.

Additionally, injection molded plates were aged for 500 hours at 130° C.and stress/strain properties measured. Melt flow rate (MFR) was measuredat 190° C. with either a 2.16 kg load (condition E) or a 5 kg load(condition P) according to ASTM D 1238.

A REICHERT heating bank was used to assess the fusion temperature of thecompounds.

Results and Discussion

The results may also be found in Table 1.

TABLE 1 Composition 01 02 03 04 Formulations: STYROFLEX BX 6105 100 3070 100 KRATON G-1652 — 70 30 — ENDEX 155 50 50 50 — TINUVIN 327 1.251.25 1.25 — IRGANOX 1010 1.00 1.00 1.00 — Properties: MD PMD MD PMD MDPMD MD PMD Tensile strength 11.9 15.7 14.3 15.6 17.4 15.1 12.9 26.6 MPaElongation at break % 350 580 390 540 200 610 460 650 Modulus 100% MPa8.2 7.0 10.7 9.7 11.0 9.3 3.9 3.5 Modulus 300% MPa 10.0 7.5 11.6 9.9 9.86.9 5.4 Modulus 500% MPa 11.8 14.3 10.6 11.8 Tear strength kN/m 91 109109 50 MFR (E) g/10 min 9 7 10 <1 Hardness (Shore D) 52 59 59 31 FusionTemp. ° C. 120 120 120 135 Composition 05 06 07 07 aged* 08Formulations: STYROFLEX BX 6105 100 30 70 70 30 KRATON G-1652 70 KRATONG-1654 30 30 70 NOVOLEN 1100 UC 20 20 20 20 TINUVIN 327 1.25 1.25 1.251.25 1.25 IRGANOX 1010 1.00 1.00 1.00 1.00 1.00 Properties: MD PMD MDPMD MD PMD MD PMD MD PMD Tensile strength 20.9 28.4 18.1 29.0 22.6 28.612.2 11.4 47.5 28.6 MPa Elongation at break % 640 680 530 571 600 680280 260 520 590 Modulus 100% MPa 6.0 4.9 3.9 2.9 5.8 5.9 8.3 8.3 5.3 4.7Modulus 300% MPa 8.6 7.6 6.6 5.3 8.1 7.3 8.8 7.4 Modulus 500% MPa 15.213.3 14.7 16.1 14.5 12.2 18.7 14.2 Tear strength kN/m 61 43 62 62 64 MFR(E) g/10 min <1 <1 <1 <1 <1 MFR (P) g/10 min 11 <1 3 <1 Hardness (ShoreD) 36 28 35 35 Hardness (Shore A) 89 79 89 92 89 Fusion Temp. °C. >200 >200 160 >200 *(>500 hrs at 130° C.)

COMPARATIVE EXAMPLE 9

A formulation similar to Composition 01 was made, wherein 100 parts byweight STYROFLEX were replaced by 100 parts by weight KRATON G. However,this material, in absence of any oil, could not be properly fused. Thisresult corresponds with comparative examples 7 and 8 of EP-A-0,811,657mentioned before.

Conclusions

The suitability of compositions 01 to 08 for use as free flowing powderhas been established on the basis of these modeling experiments.

The presence of a styrenic block copolymer of type (a1) allows thesynthesis of composition in the form of fusible powders without the useof an oil.

Compositions 01 to 03 exhibit a good balance of mechanical propertiesand have a hardness in the Shore D range. Fogging was not tested, butthis requirement is expected to be met as no plasticizer was used. Thesecompositions may be used for applications that do not require hightemperature performance. However, for slush molding these compositionsdo require some further optimization, in that their fusion temperatureis below the 130° C. required to be sufficiently heat resistant.

Likewise, Compositions 05, 06, and 08 have adequate mechanicalproperties for slush molding application, but exhibit fusiontemperatures in excess of 190° C., the typical fusion temperature.

Compositions 04 and 07, however, have fusion temperatures between 130and 190° C. and are hence immediately useful for free flowing powderapplications. In addition, the aging experiment illustrates thatComposition 07 still meets the end use requirements after 500 hours.

1. A free flowing powder composition with a particle size of less thanor equal to 800 μm consisting essentially of: (a) 100 parts by weight ofone or more styrenic block copolymers, at least one of which is a blockcopolymer (a1) comprising: at least one block S having a glasstransition temperature Tg above 25° C., which block S containspolymerized units of a vinylaromatic monomer and forms the rigid phase(c1); and at least one elastomeric block B/S having a Tg below 25° C.,which elastomeric block B/S contains polymerized units of both avinylaromatic monomer and a conjugated diene in random sequence andforms the soft phase (c2), wherein the phase volume ratio of block S toblock B/S is chosen so that the amount of the rigid phase in the totalblock copolymer is from 1 to 40% by volume and wherein the amount of theconjugated diene is less than 50% by weight on the whole of thecopolymer; and (b) no plasticizing oil.